i got one of the tank top binders from underworks a few years ago; the only binding part was the chest area and the rest was more like a snug-fitting shirt material, slightly stretchy/clingy but also kind of loose in places. it doesn't fit me well any more, so this might affect the results when i last tried it on, but what i didn't like about it last i tried to wear it was how clingy the shirt material was. i could see the "separation" of materials in where the binder part was (like a defined dip beneath the chest/binder area that made it stand out), and the shirt material hugged around my hips/belly in a way i did not care for. i'm sure that would be less of an issue if yours fits well and you wear clothing over it, but even when i first got mine i remember having some problems with it. the stiffness of the binder part was also an issue, as it didn't lay against my body in some places and would poke out awkwardly under my shirt.
i have a gc2b half-binder, the short one, and i haven't had any issues with that. it's not as stiff as the underworks one, yet i feel it actually binds better. it's more comfortable overall and i definitely prefer having less material under my clothes when i'm working. i do still want a longer one (that fits) in the future, so if/when i go for one of those i'll be sticking with this brand.
haven't tried a short binder from underworks, but i would guess that it's the same as the other, just without the clingy shirt material.